Implementing Disk Quotas
Disk space can be restricted by implementing
disk quotas which alert a system administrator before a user consumes too much
disk space or a partition becomes full.
Disk quotas can be configured for individual
users as well as user groups. This makes it possible to manage the space
allocated for user-specific files (such as email) separately from the space
allocated to the projects a user works on (assuming the projects are given
their own groups).
In addition, quotas can be set not just to
control the number of disk blocks consumed but to control the number of inodes
(data structures that contain information about files in UNIX file systems).
Because inodes are used to contain file-related information, this allows
control over the number of files that can be created.
The quota RPM must be installed to implement disk quotas.
Note
1. Configuring Disk Quotas
To implement disk quotas, use the following
steps:
1. Enable
quotas per file system by modifying the /etc/fstab file.
2. Remount
the file system(s).
3. Create
the quota database files and generate the disk usage table.
4. Assign
quota policies.
Each of these steps is discussed in detail in
the following sections.
1.1. Enabling Quotas
As root, using a text editor, edit the /etc/fstab file.
Add the usrquota and/or grpquota options to the file systems that require quotas:
/dev/VolGroup00/LogVol00
/ ext3 defaults 1 1
LABEL=/boot /boot ext3
defaults 1 2
none /dev/pts devpts
gid=5,mode=620 0 0
none /dev/shm tmpfs
defaults 0 0
none /proc proc
defaults 0 0
none /sys sysfs defaults 0 0
/dev/VolGroup00/LogVol02
/home ext3 defaults,usrquota,grpquota 1 2
/dev/VolGroup00/LogVol01
swap swap defaults 0 0 . . .
In this example, the /home file
system has both user and group quotas enabled.
Note
The
following examples assume that a separate /home partition was created during the installation of Red Hat
Enterprise Linux. The root (/) partition can be used for setting quota policies in the /etc/fstab file.
1.2. Remounting the File Systems
After adding the usrquota and/or grpquota options, remount each file system whose fstab entry
has been modified. If the file system is not in use by any process, use one of
the following methods:
- Issue
the umount command followed
by the mount command to
remount the file system.(See the manpage for both umount and mount for the specific
syntax for mounting and unmounting various filesystem types.)
- Issue
the mount -o remount <file-system> command (where <file-system> is the name of
the file system) to remount the file system. For example, to remount the /home file system, the
command to issue is mount -o remount /home.
If the file system is currently in use, the
easiest method for remounting the file system is to reboot the system.
1.3. Creating the Quota Database Files
After each quota-enabled file system is
remounted, the system is capable of working with disk quotas. However, the file
system itself is not yet ready to support quotas. The next step is to run thequotacheck command.
The quotacheck command examines quota-enabled file systems and builds a table
of the current disk usage per file system. The table is then used to update the
operating system's copy of disk usage. In addition, the file system's disk
quota files are updated.
To create the quota files (aquota.user and aquota.group) on
the file system, use the -c option of thequotacheck command.
For example, if user and group quotas are enabled for the /home file
system, create the files in the /home directory:
quotacheck
-cug /home
The -c option specifies that the quota files should be created for each
file system with quotas enabled, the -u option specifies to check for user quotas, and the -g option
specifies to check for group quotas.
If neither the -u or -g options are specified, only the user quota file is created. If
only -g is
specified, only the group quota file is created.
After the files are created, run the following
command to generate the table of current disk usage per file system with quotas
enabled:
quotacheck
-avug
The options used are as follows:
- a — Check all
quota-enabled, locally-mounted file systems
- v — Display
verbose status information as the quota check proceeds
- u — Check user
disk quota information
- g — Check group
disk quota information
After quotacheck has finished running, the quota files corresponding to the
enabled quotas (user and/or group) are populated with data for each
quota-enabled locally-mounted file system such as /home.
1.4. Assigning Quotas per User
The last step is assigning the disk quotas
with the edquota command.
To configure the quota for a user, as root in
a shell prompt, execute the command:
edquota
username
Perform this step for each user who needs a
quota. For example, if a quota is enabled in /etc/fstab for the /home partition (/dev/VolGroup00/LogVol02 in the
example below) and the command edquota testuser is executed, the following is shown in the editor configured as
the default for the system:
Disk
quotas for user testuser (uid 501):
Filesystem blocks soft
hard inodes soft
hard
/dev/VolGroup00/LogVol02 440436
0 0 37418
0 0
Note
The text
editor defined by the EDITOR environment variable is used by edquota. To
change the editor, set the EDITOR environment variable in your ~/.bash_profile file to the full path of the editor of your choice.
The first column is the name of the file
system that has a quota enabled for it. The second column shows how many blocks
the user is currently using. The next two columns are used to set soft and hard
block limits for the user on the file system. The inodes column shows how many inodes the user is currently using. The
last two columns are used to set the soft and hard inode limits for the user on
the file system.
The hard block limit is the absolute maximum
amount of disk space that a user or group can use. Once this limit is reached,
no further disk space can be used.
The soft block limit defines the maximum
amount of disk space that can be used. However, unlike the hard limit, the soft
limit can be exceeded for a certain amount of time. That time is known as the grace period. The grace period can be expressed in
seconds, minutes, hours, days, weeks, or months.
If any of the values are set to 0, that limit
is not set. In the text editor, change the desired limits. For example:
Disk
quotas for user testuser (uid 501):
Filesystem
blocks soft hard
inodes soft hard
/dev/VolGroup00/LogVol02 440436 500000
550000 37418 0
0
To verify that the quota for the user has been
set, use the command:
quota
testuser
1.5. Assigning Quotas per Group
Quotas can also be assigned on a per-group
basis. For example, to set a group quota for the develgroup
(the group must exist prior to setting the group quota), use the command:
edquota
-g devel
This command displays the existing quota for
the group in the text editor:
Disk
quotas for group devel (gid 505):
Filesystem blocks soft
hard inodes soft
hard
/dev/VolGroup00/LogVol02 440400
0 0 37418
0 0
Modify the limits, then save the file.
To verify that the group quota has been set,
use the command:
quota
-g devel
Setting the Grace Period
for Soft Limits
If soft limits are set for a
given quota (whether inode or block and for either users or groups) the grace
period, or amount of time a soft limit can be exceeded, should be set with the
command:
edquota -t
While other edquota commands
operate on a particular user's or group's quota, the -t option
operates on every filesystem with quotas enabled.
Managing Disk Quotas
If quotas are implemented,
they need some maintenance — mostly in the form of watching to see if the
quotas are exceeded and making sure the quotas are accurate.
Of course, if users
repeatedly exceed their quotas or consistently reach their soft limits, a
system administrator has a few choices to make depending on what type of users
they are and how much disk space impacts their work. The administrator can
either help the user determine how to use less disk space or increase the
user's disk quota.
2.1. Enabling and
Disabling
It is possible to disable
quotas without setting them to 0. To turn all user and group quotas off, use
the following command:
quotaoff -vaug
If neither the -u or -g options
are specified, only the user quotas are disabled. If only -g is
specified, only group quotas are disabled. The -v switch
causes verbose status information to display as the command executes.
To enable quotas again, use
the quotaon command with the same options.
For example, to enable user
and group quotas for all file systems, use the following command:
quotaon -vaug
To enable quotas for a specific
file system, such as /home, use
the following command:
quotaon -vug /home
If neither the -u or -g options
are specified, only the user quotas are enabled. If only -g is
specified, only group quotas are enabled.
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